It is known in the art that photographic display materials are utilized for advertising, as well as decorative displays of photographic images. Since these display materials are used in advertising, the image quality of the display material is critical in expressing the quality message of the product or service being advertised. Further, a photographic display image needs to be high impact, as it attempts to draw consumer attention to the display material and the desired message being conveyed. Typical applications for display material include product and service advertising in public places such as airports, buses and sports stadiums, movie posters, point of purchase areas such as store fronts, illuminate billboards and fine art photography. The desired attributes of a quality, high impact photographic display material are a slight blue density minimum, durability, sharpness, and flatness. Cost is also important, as display materials tend to be expensive compared with alternative display material technology, mainly lithographic images on paper. For display materials, traditional color paper is undesirable, as it suffers from a lack of durability for the handling, photoprocessing, and display of large format images.
In the formation of color paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult, requiring great care and expense to ensure proper laydown and cooling of the polyethylene layers. The formation of a suitably smooth surface would also improve image quality, as the display material would have more apparent blackness as the reflective properties of the improved base are more specular than the prior materials. As the whites are whiter and the blacks are blacker, there is more range in between and, therefore, contrast is enhanced. It would be desirable if a more reliable and improved surface could be formed at less expense.
Prior art photographic transmission display materials with incorporated diffusers have light sensitive silver halide emulsions coated directly onto a gelatin coated clear polyester sheet. Incorporated diffusers are necessary to diffuse the light source used to illuminate transmission display materials. Without a diffuser, the light source would reduce the quality of the image. Typically, white pigments are coated in the bottom most layer of the imaging layers. Since light sensitive silver halide emulsions tend to be yellow because of the gelatin used as a binder for photographic emulsions, minimum density areas of a developed image will tend to appear yellow. A yellow density minimum reduces the commercial value of a transmission display material because the imaging viewing public associates image quality with a white density minimum. It would be desirable if a transmission display material with an incorporated diffuser could have a more blue density minimum which people perceptually prefer.
It has been proposed in U.S. Pat. No. 5,212,053 to use a cellulose paper base with a basis weight less than 120 g/m.sup.2 as a support for a photographic translucent display material. In U.S. Pat. No. 5,212,053 numerous advantages are obtained by the use of cellulose paper as a base. Advantages such as the low cost of paper compared to suitable polymer bases and an increase in manufacturing efficiency gained by the use of color photographic paper forming apparatus were disclosed. While all of these improvements are possible with the use of a melt cast extruded polyethylene paper base, the paper base does not have the required strength properties to be reliability processed in wet chemistry common with the imaging development process.
Typically transmission display materials require more saturated colors so they appear as true colors to the viewer. In a photographic system, it is common to coat up 2 to 2.5 times the normal coverage of a reflection print. This added coverage contains gelatin. When gelatin is dried after the processing operation, there is a large force exerted on the base because of the shrinkage forces within the gelatin structure. On melt cast polyethylene paper, this force can cause the paper imaging element to curl excessively and crease making the element unusable. When the illuminated photographic display materials are processed utilizing weak paper and low strength polyethylene layers, the web can break causing a loss in efficiency in commercial photoprocessing labs. Further, the thin papers disclosed in U.S. Pat. No. 5,212,053 are not strong enough for efficient transport in digital printing equipment such as ink jet printers or thermal dye transfer printers. It would be desirable if translucent display material with a cellulose paper base had the required strength properties for efficient transport through digital printers, yet was thin enough to exhibit the required transmission properties. The paper disclosed in U.S. Pat. No. 5,212,053, while providing a good display material when coated with a gelatin based silver halide photographic emulsion and placed in a low relative humidity environment, has a tendency to curl towards the image side. This may create some difficulties during mounting of this display material. Excessive curl can cause problems in handling and constraining the display material which may cause damage and distract from its commercial value. It would be desirable to have a paper base transmission material that has less curl and handles better than prior art materials.
Prior art photographic transmission display materials with incorporated diffusers have light sensitive silver halide emulsions coated directly onto a gelatin subbed clear polyester sheet. TiO.sub.2 is added to the bottom most layer of the imaging layers to diffuse light so that individual elements of the illuminating bulbs utilized are not visible to the observer of the displayed image. However, coating TiO.sub.2 in the imaging layer causes manufacturing problems such as increased coating coverage which requires more coating machine drying and a reduction in coating machine productivity as the TiO.sub.2 requires additional cleaning of the coating machine. Further, as higher amounts of TiO.sub.2 are used to diffuse high intensity illumination systems, the TiO.sub.2 coated in the bottom most imaging layer causes unacceptable light scattering reducing the quality of the transmission image. It would be desirable to reduce or eliminate the TiO.sub.2 from the image layers while providing the necessary transmission properties and image quality properties.
Prior art photographic transmission display material use polyester as a base for the support. Typically the polyester support is from 150 to 250 .mu.m thick to provide the required stiffness. A cellulose paper base material would be lower in cost and allow for roll handling efficiency, as the rolls would weigh less and be smaller in diameter. It would be desirable to use a low cost base material that had the required stiffness but was thinner to reduce cost and improve roll handling efficiency.
Prior art photographic transmission display materials, while providing excellent image quality, tend to be expensive when compared with other quality imaging technologies such as ink jet imaging, thermal dye transfer imaging, and gravure printing. Since photographic transmission display materials require an additional imaging processing step compared to digital imaging systems such as ink jet printing and thermal dye transfer printing, the cost of a transmission photographic display can be higher than digital imaging systems. The processing equipment investment required to process photographic transmission display materials also requires consumers to typically interface with a commercial processing lab, increasing time required to move from concept to image. It would be desirable if a high quality transmission display support could utilize nonphotographic quality imaging technologies.
Photographic transmission display materials have considerable consumer appeal as they allow images to be printed on high quality support for home or small business use. Consumer use of photographic display materials generally have been cost prohibitive since consumers typically do not have the required volume to justify the use of such materials. It would be desirable if a high quality transmission display material could be used in the home without a significant investment in equipment to print the image